Effect of Block Copolymer Concentration and Water-Ethanol Ratio on Phase Transitions of Pluronics Using Molecular Dynamics Simulations

Pluronics, also known as poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (BCP), are recognized for their ability to self-assemble into diverse mesophases, making them valuable in designing materials with tailored properties for applications in drug delivery and nanotechnology. Although the formation of these self-assembled structures is achieved by the widely utilized method of modulating the solvent-cosolvent composition, a comprehensive understanding of their underlying mechanism and phase transition behavior still remains elusive. Here, we used coarse-grained molecular dynamics simulations to explore the self-assembly of different triblock copolymers in a water/ethanol mixture with different compositions. The investigation includes an exploration of the impact of BCP concentration and the PPO/PEO block ratio on cosolvent-induced self-assembly. The outcomes unveil a diverse array of mesophases formed by BCP within the ternary BCP/water/ethanol mixture. We observed that the cosolvent-induced morphological transitions are governed by the selective affinity of PPO and PEO blocks toward the solvent and cosolvent. It also alters the local chemical environment and conformational changes in individual BCP chains. Additionally, we find that the influence of solvent-cosolvent composition is significant at low BCP composition, instigating an unimeric-to-micellar phase transition, while at high BCP composition, the PPO/PEO block ratio dominates the effect of solvent-cosolvent composition and determines the self-assembled morphology. Our results offer fundamental insights, serving as a guide to control the morphology of BCP self-assembly by fine-tuning the solvent-cosolvent ratio.